Inter-axle differential and method for operation of said inter-axle differential

ABSTRACT

Methods and systems for a locking mechanism in an inter-axle differential are provided. A vehicle system, in one example, includes an electric motor coupled to a clutch assembly in a locking mechanism of an inter-axle differential coupled to a first axle and a second axle, the clutch assembly is configured to selectively disengage the locking mechanism, and in the disengaged configuration the locking mechanism permits speed differentiation between the first and second axles. The system further includes an electric motor brake coupled to the electric motor and configured to selectively apply a brake torque to the electric motor and the electric motor is configured to actuate the clutch assembly.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 17/028,642, entitled “INTER-AXLE DIFFERENTIAL AND METHOD FOROPERATION OF SAID INTER-AXLE DIFFERENTIAL,” and filed on Sep. 22, 2020.The entire contents of the above-listed application are herebyincorporated by reference for all purposes.

TECHNICAL FIELD

The present disclosure generally relates to a system with an inter-axledifferential with a locking mechanism and a method for operation of theinter-axle differential.

BACKGROUND AND SUMMARY

Some vehicle transmissions have employed inter-axle differentials (IADs)which may allow speed differentiation between multiple axles, such astandem rear axles. Locking mechanisms may be used in certain IADs toprevent speed differentiation between the axles and increase vehicletraction during selected conditions. Some of the locking mechanisms havemade use of dog clutches with constrained windows of operation. Forinstance, periods during which the IAD may perform locking and unlockingmay be constrained by vehicle speed. Certain IADs may demand that thevehicle remain stationary or travel at a relatively low speed to performlocking and unlocking procedures in the IAD. Consequently, the vehicleoperator may lock the IAD when they anticipate a reduction in vehicletraction. The IAD may remain unlocked in certain situations, such aswhen traction drops unexpectedly or the vehicle operator overlooksindicators of reduced traction conditions, for instance. Furthermore,the back-driving torque experienced at the IAD may be larger thanback-driving torque experienced by downstream axle differentials. Therelatively large back-driving torque at the IAD may increase componentloading, in some cases.

To overcome at least some of the aforementioned challenges a vehiclesystem is provided. The vehicle system, in one example, includes anelectric motor coupled to a clutch assembly in a locking mechanism of aninter-axle differential (IAD) coupled to a first axle and a second axle.In the system, the clutch assembly is configured to selectivelydisengage the locking mechanism. In a disengaged configuration, thelocking mechanism permits speed differentiation between the first andsecond axles. The system further includes an electric motor brakecoupled to the electric motor and configured to selectively apply abrake torque to the electric motor. The electric motor is configured toactuate the clutch assembly. In this way, a compact actuator can provideactuation functionality for a friction clutch that may engage over awider range of vehicle operating conditions. For instance, engagement ordisengagement of the friction clutch may take place based on operatingconditions such as vehicle traction. Consequently, the IAD achievesactive locking and unlocking functionality that may unfold while thevehicle is in motion, if desired. By incorporating the brake into theIAD, the chance of unwanted electric motor back-driving may besignificantly reduced (e.g., substantially eliminated, in somescenarios). Thus, holding the motor's output torque at a relatively highvalue to counteract back-driving can be avoided, if wanted, whichincreases system efficiency.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic representation of a vehicle system including aninter-axle differential (IAD) coupled to multiple drive axles.

FIG. 2 shows a side view of an embodiment of vehicle system with an IAD.

FIG. 3 shows a perspective view of the vehicle system with the IAD,illustrated in FIG. 2.

FIG. 4 shows an exploded view of the vehicle system with the IAD,illustrated in FIG. 2.

FIG. 5 shows a cross-sectional view of the vehicle system with the IAD,illustrated in FIG. 2.

FIG. 6 shows a method for operation of a vehicle system including anIAD.

FIGS. 2-5 are drawn approximately to scale. However, other relativedimensions may be used, if desired.

DETAILED DESCRIPTION

Vehicle drivetrain system embodiments are described herein. Thedrivetrain system includes an inter-axle differential (IAD) that may bedesigned with active locking functionality. The IAD may thereforeinclude a locking mechanism actuated by an electric motor. To engage thelocking mechanism, the electric motor may drive a clutch assembly, whichmay couple a gear in the clutch to an input shaft in the differential.After the clutch is engaged, a motor brake may be operated to sustainthe IAD in the locked configuration and prevent motor back-driving. Themotor brake may be attached to a housing of the IAD and reacted by thehousing. Specifically, in one example, the electric motor may axiallyextend away from a yoke or other input interface of the IAD. Therelative position of the motor with regard to the IAD's input enablesthe IAD to form a compact arrangement. The IAD may therefore presentfewer vehicle packaging challenges and provide greater adaptability withregard to vehicle design and manufacture, if wanted.

With regard to the drawings, FIG. 1 schematically depicts a vehicleincluding an IAD with active locking and unlocking functionality. FIGS.2-3 illustrate an embodiment of an IAD with a motor and motor brakedesigned to space efficiently engage and disengage the IAD's lockingfeature. FIGS. 4 and 5 show cross-sectional and exploded views of thelocking mechanism with a clutch assembly configured to actively lock andunlock the IAD. FIG. 6 shows a method for operation of an IAD toefficiently initiate and sustain locking engagement and disengagement,if so desired.

FIG. 1 shows a schematic diagram of a vehicle 100. The vehicle 100 maycomprise a drive device 102 which may generate rotational output such asan internal combustion and/or an electric motor. The internal combustionengine may include conventional components such as cylinder(s),piston(s), valves, a fuel delivery system, an intake system, an exhaustsystem, etc. and the electric motor may include conventional componentssuch as a rotor, stator, housing, and the like. The vehicle may take avariety of forms such as a light, medium, or heavy duty vehicle.Furthermore, hybrid and battery electric vehicles have been envisioned.In other examples, the vehicle may solely use an internal combustionengine for motive power generation.

The diagram of FIG. 1 provides a higher-level topology of the vehicle,drivetrain, and corresponding components. Nevertheless, the vehicle,drivetrain, and corresponding components may have greater structuralcomplexity than is captured in FIG. 1. The structural details of variousfacets of a vehicle system with an IAD are described in greater detailherein with regard to FIGS. 2-5.

The drive device 102 may couple to a vehicle system 104 via a shaft 106or other suitable mechanical components. The vehicle system 104 may bedesigned to transfer torque to drive wheels in a first axle 108 and asecond axle 110. The system may make use of mechanical components suchas shaft, gears, bearing, and the like to accomplish the aforementionedtorque transfer functionality. The vehicle system 104 includes an IAD112. The IAD 112 includes several components such as a locking mechanism114 that may comprise an actuation system 116. The actuation system 116may include an electric motor 118, an electric motor brake 120, a clutchactuator 122, and a clutch assembly 124 (e.g., a friction clutch).

The electric motor 118 may generate a rotational output to induceengagement and disengagement of the locking mechanism 114, duringselected periods. To elaborate, the electric motor 118 may driveoperation of the clutch actuator 122. In turn, the clutch actuator 122may be configured to engage and disengage the clutch assembly 124. Thesystem may utilize a variety of components such as ball ramps, gears,plates, etc. in the clutch actuator for engagement-disengagementoperation. The clutch assembly 124, when engaged, may prevent speeddifferentiation between outputs provided to the first and second axles108, 110. Conversely, when the clutch assembly 124 is disengaged, thesystem may allow for speed differentiation between the first and secondaxles 108, 110. It will be appreciated that speed differentiation allowsthe rotational speeds of the axles 108, 110 to vary in relation to oneanother, during certain conditions. More generally, when the lockingmechanism 114 operates in an engaged configuration, the system inhibitsspeed differentiation between the first and second axles 108, 110. Inthis way, vehicle traction may be increased when the vehicle isoperating in low traction environments (e.g., wet, snowy, and/or muddyroads), for example. To elaborate, when the locking mechanism inhibitsspeed differentiation between the axles, the chance of the traction ofthe first and second axles dropping below a desired value is reduced,when compared to vehicles with only locking axle differentials.

The electric motor 118 may include a rotor, a stator, an output shaft, ahousing, and the like to generate rotational output. The electric motorbrake 120 may rotationally couple to the electric motor 118 and modulatebrake torque used to slow or prevent rotation of the motor's outputshaft. Further, the motor brake 120 may be arranged on an axial side ofthe motor 118 opposite the motor's output shaft, to reduce thelikelihood of the brake spatially interfering with upstream propulsionsystem components. The electric motor brake 120 may be anelectromagnetic brake or an eddy current brake electromagneticallyapplying brake torque to the electric motor. Thus, the brake may includediscs, magnets, etc. to modulate electric motor speed. In such anexample, the brake may be electrically actuated. In another example, themotor brake 120 may be a friction brake which may be electrically,hydraulically, or pneumatically actuated. The motor brake may beactivated during selected periods to hold the locking mechanism 114 inan engaged configuration, for example. In this way, the likelihood ofback-driving of the electric motor 118 may be reduced. Thus, motorback-driving may be avoided in certain cases, which may increase motorlongevity.

The IAD 112 may couple to the first and second axles 108, 110. The axlecoupling may be accomplished via shafts and/or gears, for instance.Thus, the IAD 112 may include a first rotational output (e.g., driveshaft coupled one of the axle differential) and a second rotationaloutput (e.g., a gear coupled a carrier of the other axle differential).Unlocking and locking the IAD may therefore permit and inhibit speeddifferentiation between these two rotational outputs.

The first and second axles 108, 110, in turn may include a first and asecond axle differential 126, 128, respectively. The first and secondaxle differentials 126, 128 may enable speed differentiation betweendrive wheels of the corresponding axle under certain conditions. In someimplementations, the axle differentials may be locking differentialsconfigured to inhibit and permit wheel speed differentiation atdifferent times. However, a variety of suitable types of axledifferential may be deployed in the vehicle. The first and second axles108, 110 may be in a tandem axle arrangement spaced away fromnon-driving steerable axle (e.g., non-driving front axle). In anotherexample, the first axle 108 may be a front axle and the second axle 110may be a rear axle.

The first axle 108 may include axle shafts 130 coupled to drive wheels132. The second axle 110 likewise may include axle shafts 134 and drivewheels 136. The vehicle system 104 may include a shaft 138 which extendsbetween the IAD 112 and the second axle 110.

The vehicle 100 may include a control system 150 with a controller 152.The controller 152 may comprise a processor 154 and memory 156. Thememory 156 may hold instructions stored therein that when executed bythe processor cause the controller to perform the various methods,control techniques, etc., described herein. The processor 154 mayinclude a microprocessor unit and/or other types of circuits. The memory156 may include data storage mediums such as random access memory, readonly memory, keep alive memory, combinations thereof, etc. Furthermore,the memory 156 may include non-transitory memory.

The controller 152 may receive various signals from sensors 158 in thevehicle 100 and the vehicle system 104. The sensors may include avehicle speed sensor 170, a vehicle load sensor 172, an IAD sensor 159,and the like. The controller 152 may send control signals to variousactuators 160 coupled at different locations in the vehicle 100 andvehicle system 104. For instance, the controller may send signals to theIAD 112 to lock and unlock the IAD to inhibit and permit speeddifferentiation between the first and second axles 108, 110. The IAD maylock and unlock responsive to driver input, in one example. Forinstance, the vehicle 100 may include an input device 162 (e.g., button,switch, touch interface, touch panel, keyboard, combinations thereof,etc.). The input device 162 may generate an IAD lock or unlock requestin response to driver input. Thus, a vehicle operator may manipulate theinput device 162 to initiate IAD locking and unlocking operation.Additionally or alternatively, the IAD may automatically lock and unlockusing an automated strategy. Entry condition parameters for IAD lockingand unlocking may include vehicle speed, wheel traction, ambient weatherconditions (e.g., ambient temperature, humidity, etc.), and/orcombinations thereof. The other controllable components in the vehiclesystem may function in a similar manner with regard to command signalsand actuator adjustment.

An axis system 190 is provided in FIG. 1 as well as FIGS. 2-5, forreference. The z-axis may be a vertical axis, the x-axis may be alateral axis, and/or the y-axis may be a longitudinal axis, in oneexample. However, the axes may have other orientations, in otherexamples.

FIG. 2 illustrates a vehicle system 200 with an IAD 202. The vehiclesystem 200 and IAD 202, shown in FIG. 2, may serve as an example of thevehicle system 104 and IAD 112, depicted in FIG. 1. The vehicle system200 may include an input interface 204. The input interface 204 isillustrated as a yoke in FIG. 2. However, other suitable types ofmechanical components may operate as an input for the IAD, in otherembodiments. For instance, the IAD may include a splined shaft, a gear,a drive chain, and the like for power input. The IAD may further includeoutput interfaces 206 configured to provide torque to axles, such as thefirst and second axles 108, 110 shown in FIG. 1. To elaborate, one ofthe output interfaces 206 may be coupled to drive shaft transferringpower to a first axle differential and the other output interface may becoupled a second axle differential attached (e.g., directly attached) tothe IAD. However, the IAD may deploy other suitable types of outputinterfaces in alternate embodiments, such as a gear, a belt, a chain,and the like. The IAD 202 may include a housing 208 that may enclose alocking mechanism 404, shown in FIGS. 4 and 5, as well as othercomponents such as shafts and gears which transfer torque between theinput interface 204 from the output interfaces 206. The housing 208 mayinclude a section 210 at least partially enclosing gears coupled to aclutch actuator, described in greater detail herein. The IAD housingsection 210 may removably couple to a motor housing body 211 via bolts213 or other suitable attachment devices. In this way, personnel mayefficiently access actuator gearing during servicing and repair, forexample. The housing section 210 may include a flange 217 which may beoriented in a plane substantially perpendicular to the rotational axis250. When the motor's housing body 211 is coupled to a flange in thisarrangement, motor torque may be efficiently reacted by the IAD housing.

The IAD 202 may further include an electric motor 212. The electricmotor 212 may couple to the housing section 210 via bolts 215 or othersuitable devices. The electric motor 212 may serve as an actuator for aclutch assembly in a locking mechanism, described in greater detailherein. Thus, rotation of the motor's output shaft in oppositerotational directions may initiate locking and unlocking operation inthe IAD. An electric motor brake 214 may couple to the electric motor212 and is designed to selectively apply brake torque to the electricmotor. The brake may be formed as an electromagnetic brake withcomponents such as coils, permanent magnets, etc., or may be a frictionbrake as previously discussed. Engagement of the brake 214 may occurwhile the differential remains locked. In this way, the chance of motorback-driving may be significantly reduced while differential lockingpersists.

FIG. 2 indicates a rotational axis 250 of the electric motor 212 andmotor brake 214 is along with a rotational axis 252 of the inputinterface 204. The rotational axes 250, 252 are further indicated inFIGS. 3-5, when appropriate, for reference. The electric motor 212 andmotor brake 214 both axially extend away from the input interface 204(e.g., the yoke) to achieve a compact arrangement. Electric motor 212and motor brake 214 may be arranged vertically above and/or laterallyoffset from the input interface 204. The relative arrangement betweenthe input interface and the electric motor may further increase theIAD's packaging efficiency. Thus, IAD may achieve a space efficient formwhich may create fewer packaging challenges in the vehicle's designprocess. The IAD's applicability may therefore be expanded, due to theIAD's space efficient form. Other vehicle systems such as a suspensionsystem may be less space constrained due to the IAD's space efficientprofile.

The electric motor 212 and the motor brake 214 may receive commands froma controller, such as the controller 152 shown in FIG. 1. Thus, thecontrol schemes discussed in greater detail herein may be deployed inthe IAD 202 shown in FIG. 2.

FIG. 3 shows a perspective view of the vehicle system 200 with the IAD202. FIG. 3 again illustrates the electric motor 212, the motor brake214, the IAD housing 208, and the input interface 204.

FIG. 3 further depicts a clutch assembly 300 which may be included inthe IAD 202. The clutch assembly 300 may comprise an actuator ring 302with teeth 304. The clutch assembly 300 may include a spur gear 306,which forms a mesh with the actuator ring 302. As depicted, the spurgear 306 acts as an intermediary between an output shaft 308 of theelectric motor 212 and the clutch assembly 300. In this way, a compactgear arrangement may reside between the motor 212 and the clutchassembly 300. Specifically, in one example, the spur gear may be thesole gear between the motor's output and the actuator ring. The motor'shousing may be more space efficiently coupled to the IAD housing andreacted there through due to the compact gear arrangement. The spur gear306 axially extends towards the body 211 of the motor 212, which createsfurther gains in packaging efficiency. An actuation plate 312 of thespur gear 306 may serve as a motor attachment interface. The actuationplate 312 may extend below the teeth 304 of the actuator ring 302 tofurther increase IAD space efficiency. A cover plate 313 attached to theIAD housing section 210 may also be included in the IAD, in one example.The cover plate 313 may serve to partially enclose the actuationassembly and may provide a rotational attachment point for the actuationplate 312 and/or spur gear 306.

FIG. 4 shows a cross-sectional view of the IAD 202. The input interface204 coupled to an input shaft 400 is depicted in FIG. 4. A bearing 402may couple to the input shaft 400. The bearing supports and enablesrotation of the shaft. The bearing 402 is depicted as a thrust rollerbearing, which reacts axial and radial loads. However, other suitabletypes of bearings may be used such as a ball bearing, in otherembodiments.

FIG. 4 depicts the clutch assembly 300 in the IAD 202. The clutchassembly 300 may be included in a locking mechanism 404 which may beconfigured to engage and disengage locking in the IAD 202. The clutchassembly 300 may comprise a ball ramp actuator 405 with an actuationplate 406 coupled to the actuator ring 302, shown in FIG. 3. Thus, whenthe motor rotates the actuator ring, the actuation plate 406 maycorrespondingly rotate. A ball 408 residing in ramps in the actuationplate 406 may function to axially engage and disengage a disc pack 410in the clutch assembly 300. The disc pack 410, when engaged,rotationally couples a gear 412 (e.g., a helical gear) to the inputshaft 400. The gear 412 may transfer torque to an axle differential(e.g., the axle differential 126, shown in FIG. 1).

The input shaft 400 may further couple to a side gear 414 in the IAD202. In turn, the side gear 414 meshes with spider gears 416 on acarrier 418. Teeth 420 on an axial side 422 of the gear 412 may form amesh with the spider gears 416. The aforementioned gear arrangement,permits speed differentiation between two axles (e.g., axles 108, 110,shown in FIG. 1) when the IAD 202 is in an unlocked state. The side gear414 may rotationally couple to an output shaft 415 with the outputinterface 206. As previously discussed, the output interface 206 maytransfer torque to a second drive axle (e.g., the differential 128 ofthe axle 110, shown in FIG. 1).

FIG. 5 shows an exploded view of the clutch assembly 300 in the lockingmechanism 404. The assembly 300 may include the bearing 402, the ballramp actuator 405, the disc pack 410, gear 412, spider gears 416,carrier 418, and/or side gear 414. FIG. 5 further illustrates a section500 of the input shaft 400 and a retainer 502. The ball ramp actuator405 may be in face sharing contact with the retainer 502. The ball rampactuator 405, while actuation unfolds, moves axially in a directionalong axis 252 responsive to input from the motor 212, shown in FIG. 3.

Continuing with FIG. 5, the axial movement of the ball ramp actuator 405may move the retainer 502 which compresses and decompresses a wavespring 504 downstream of the retainer 502. Compression and decompressionof the wave spring 504 may cause axial movement of a plate 506. In turn,axial movement of the plate 506 may engage and disengage clutch discs507 and plates 509 in the disc pack 410. To elaborate, external teeth ofthe clutch plates 509 may spline to a component 511. Additionally,internal teeth of the clutch discs 507 may spline to the gear 510coupled to the input shaft section 500. While the clutch assembly 300remains engaged, the gear 412 and the input shaft 400 may rotate as oneunit. Conversely, while the clutch assembly 300 remains disengaged, thegear 412 and the input shaft 400 may rotate relative to each other.Downstream of the input shaft 400 and gear 412, power may flow from thespider gear 416 to the side gear 414.

The IAD described herein enables a compact actuation package to activelylock and unlock speed differentiation in the differential. While the IADis locked, the motor brake coupled to the actuation motor may reduce orin some cases substantially eliminate motor back-driving, which drivesdown the likelihood of unwanted motor degradation. The reduction orelimination of motor back-driving may be particularly beneficial in theIAD which may experience higher torque than downstream axledifferentials. Further, the IAD may realize increased packagingefficiency due to the off-axis positioning of the motor and brake, ifwanted.

FIG. 6 shows a method 600 for operation of an electric drive axlesystem. One or more of the electric drive axle systems, components,etc., described above with regard to FIGS. 1-5, may implement method600, in one embodiment. However, other suitable electric drive axlesystems may carry out the method, in other embodiments. Furthermore, acontroller (e.g., controller 152 shown in FIG. 1) holding instructionsstored in non-transitory memory executable by a processor may be used tocarry out the steps of method 600.

At 602, the method includes determining operating conditions. Theoperating conditions may include locking device configuration, inputinterface configuration, vehicle speed, vehicle load, etc. The operatingconditions may be determined based on sensor signals, modelingalgorithms, etc.

Next at 604, the method includes determining if a state change of thelocking device is desired. The state change of the locking device mayinclude transitioning the locking device from an engaged state to adisengaged state or vice versa. User interaction with an input devicewhich indicates the driver's desire for a state change, may triggerreconfiguration of the IAD locking mechanism. However, the vehiclesystem may deploy automated strategies for triggering a locking devicestate change, in other implementations. In one instance, transitioningthe IAD from an unlocked state to a locked state may be initiated basedon vehicle traction. Vehicle traction may be calculated based onparameters such as wheel speed, vehicle speed, ambient temperature, andthe like. Thus, in one use-case implementation, the IAD may lock whenvehicle traction falls below a threshold value. It will be appreciatedthat the IAD may be an active IAD designed to lock while the vehicle istraveling between 0 kilometers per hour (km/h) and 32 km/h, in one usecase example. Further, in one example, the IAD locking mechanism maylock and prevent speed differentiation between the axles when a speedbetween the first and second axles (e.g., tandem forward and rear axles)is equal to or greater than zero. In this way, the window of vehicleoperating conditions during which the IAD can be locked may be expandedin comparison to locking devices demanding that the vehicle be stoppedor traveling below a comparatively low speed (e.g., 10 km/h) to initiatelocking operation.

If it is determined that an IAD locking device state change is notdesired (NO at 604) the method moves to 606, where the method includesmaintaining the vehicle system's current operating strategy. Forexample, a locked or unlocked state of the IAD may be sustained tomaintain the system's current operating strategy.

Conversely, if the IAD locking device is slated to transition from thedisengaged state to the engaged state, the method moves to 608. At 608,the method includes transitioning the IAD into a locked state from anunlocked state. Transitioning the IAD into a lock state includesoperating the electric motor to engage the clutch assembly, at 610, andactivating the motor brake to sustain the clutch assembly engagement, at612. Further in one example, the motor may be de-energized once themotor brake is activated. In this way, IAD locking may actively unfoldand the electric motor brake operation may maintain the IAD in thelocked state to reduce the likelihood of motor back-driving.Consequently, the chance of motor degradation is decreased.

If the IAD locking device is slated to transition from the engaged stateto the disengaged state, the method moves to 614. At 614, the methodincludes transitioning the IAD into the unlocked state from the lockedstate. This modal transition includes at 616, deactivating the motorbrake and at 618, operating the electric motor to disengage the clutchassembly. Method 600 allows the IAD to efficiently sustain lockingoperation using the brake device and reduce or eliminate the chance ofmotor back-driving. The vehicle system may achieve a robust arrangementthat may be less susceptible to higher back-driving torque experiencedby the IAD, in relation to the back-driving torque experienced by axledifferentials, for instance.

The technical effect of the vehicle system with the IAD and the methodfor operation of the system described herein is to reduce the chance ofelectric motor back-driving while the IAD is locked, which decreases thechance of motor degradation. The IAD system described herein may have acompact arrangement which increases the IAD's applicability. The IADsystem may therefore be used in a wider variety of vehicle platforms, ifso desired.

FIGS. 1-5 show example configurations with relative positioning of thevarious components. If shown directly contacting each other, or directlycoupled, then such elements may be referred to as directly contacting ordirectly coupled, respectively, at least in one example. Similarly,elements shown contiguous or adjacent to one another may be contiguousor adjacent to each other, respectively, at least in one example. As anexample, components laying in face-sharing contact with each other maybe referred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example. Asyet another example, elements shown above/below one another, at oppositesides to one another, or to the left/right of one another may bereferred to as such, relative to one another. Further, as shown in thefigures, a topmost element or point of element may be referred to as a“top” of the component and a bottommost element or point of the elementmay be referred to as a “bottom” of the component, in at least oneexample. As used herein, top/bottom, upper/lower, above/below, may berelative to a vertical axis of the figures and used to describepositioning of elements of the figures relative to one another. As such,elements shown above other elements are positioned vertically above theother elements, in one example. As yet another example, shapes of theelements depicted within the figures may be referred to as having thoseshapes (e.g., such as being circular, straight, planar, curved, rounded,chamfered, angled, or the like). Additionally, elements co-axial withone another may be referred to as such, in one example. Further,elements shown intersecting one another may be referred to asintersecting elements or intersecting one another, in at least oneexample. Further still, an element shown within another element or shownoutside of another element may be referred as such, in one example. Inother examples, elements offset from one another may be referred to assuch.

The invention will be further described in the following paragraphs. Inone aspect, a vehicle system is provided that comprises an electricmotor coupled to a clutch assembly in a locking mechanism of aninter-axle differential, wherein the inter-axle differential is coupledto a first axle and a second axle and the clutch assembly is configuredto selectively disengage the locking mechanism, and, in the disengagedconfiguration, the locking mechanism permits speed differentiationbetween the first and second axles; and an electric motor brake coupledto the electric motor and configured to selectively apply a brake torqueto the electric motor, wherein the electric motor is configured toactuate the clutch assembly.

In another aspect, a method for operation of a vehicle system isprovided that comprises operating an electric motor coupled to a clutchassembly to engage a locking mechanism in an inter-axle differential,wherein the inter-axle differential is coupled to a first axle and asecond axle and engagement of the locking mechanism prevents speeddifferentiation between the first axle and the second axle; andactivating an electric motor brake coupled to the electric motor toapply a brake torque to the electric motor and prevent back-driving ofthe electric motor. In one example, the method may further comprisedeactivating the electric motor brake to release the brake torque; andoperating the electric motor to disengage the locking mechanism, whereindisengagement of the locking mechanism enables speed differentiationbetween the first and second axles.

In yet another aspect, a vehicle system is provided that comprises avehicle system, comprising: an electric motor coupled to a clutchassembly in a locking mechanism of an inter-axle differential, whereinthe inter-axle differential is coupled to a first axle and a secondaxle, wherein the clutch assembly selectively disengages the lockingmechanism, and wherein in a disengaged configuration the lockingmechanism allows speed differentiation between the first and secondaxles; and an electromagnetic motor brake coupled to the electric motorand configured to selectively apply a brake torque to the electricmotor, wherein the electric motor is configured to actuate the clutchassembly; wherein the clutch assembly includes a ball ramp actuatorconfigured to selectively engage and disengage a plurality of frictionplates; and wherein a portion of the plurality of friction plates arerotationally coupled to a clutch configured to engage and disengage agear on an input shaft.

In any of the aspects or combinations of the aspects, the clutchassembly may include a ball ramp actuator configured to selectivelyengage and disengage a plurality of friction plates, wherein a portionof the plurality of friction plates are rotationally coupled to a clutchconfigured to engage and disengage a gear on an input shaft.

In any of the aspects or combinations of the aspects, the vehicle systemmay further comprise a spur gear coupled to the electric motor and theball ramp actuator.

In any of the aspects or combinations of the aspects, the electric motorbrake may an electromagnetic brake.

In any of the aspects or combinations of the aspects, the electric motorand the electric motor brake may extend axially away from an inputinterface.

In any of the aspects or combinations of the aspects, the vehicle systemmay further comprise a controller including executable instructionsstored in non-transitory memory that, when a speed between the first andsecond axles is equal to or greater than zero, cause the controller to:engage the locking mechanism to prevent speed differentiation betweenthe first axle and the second axle.

In any of the aspects or combinations of the aspects, the lockingmechanism may be automatically engaged based on one or more operatingconditions.

In any of the aspects or combinations of the aspects, the lockingmechanism may be engaged responsive to actuation of an input device.

In any of the aspects or combinations of the aspects, the first andsecond axles may be rear axles.

In any of the aspects or combinations of the aspects, the clutchassembly may include a ball ramp actuator configured to selectivelyengage and disengage a plurality of friction plates, wherein a portionof the plurality of friction plates may be rotationally coupled to aclutch configured to engage and disengage a gear on an input shaft.

In any of the aspects or combinations of the aspects, the electric motorand the electric motor brake may be coupled to an inter-axledifferential housing and axially extend away from an input yoke.

In any of the aspects or combinations of the aspects, the vehicle systemmay further comprise a controller including executable instructionsstored in non-transitory memory that cause the controller to: engage thelocking mechanism to prevent speed differentiation between the firstaxle and the second axle.

In any of the aspects or combinations of the aspects, the lockingmechanism may be automatically engaged based on one or more operatingconditions.

In any of the aspects or combinations of the aspects, the lockingmechanism may be engaged responsive to actuation of an input device.

In any of the aspects or combinations of the aspects, the vehicle systemmay further comprise a spur gear coupled to the electric motor and theball ramp actuator.

In any of the aspects or combinations of the aspects, the spur gear maybe directly coupled to the ball ramp actuator.

In another representation, an inter-axle differential (IAD) assembly isprovided that includes an electric motor and brake unit triggeringlocking and unlocking of a friction clutch in a body of the IAD, whereinthe brake unit holds a rotational shaft in the electric motor stationarywhile the IAD operates in a locked configuration to inhibit speeddifferentiation between a first axle and a second axle and where thefirst and second axles each include an axle differential.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevant artsthat the disclosed subject matter may be embodied in other specificforms without departing from the spirit of the subject matter. Theembodiments described above are therefore to be considered in allrespects as illustrative, not restrictive.

Note that the example control and estimation routines included hereincan be used with various drivetrain and/or vehicle systemconfigurations. The control methods and routines disclosed herein may bestored as executable instructions in non-transitory memory and may becarried out by the control system including the controller incombination with the various sensors, actuators, and other vehiclehardware. Further, portions of the methods may be physical actions takenin the real world to change a state of a device. The specific routinesdescribed herein may represent one or more of any number of controlstrategies. As such, various actions, operations, and/or functionsillustrated may be performed in the sequence illustrated, in parallel,or in some cases omitted. Likewise, the order of processing is notnecessarily required to achieve the features and advantages of theexample examples described herein, but is provided for ease ofillustration and description. One or more of the illustrated operations,actions, and/or functions may be repeatedly performed depending on thestrategy being used. Further, the described operations, actions, and/orfunctions may graphically represent code to be programmed intonon-transitory memory of the computer readable storage medium in thevehicle control system, where the described actions are carried out byexecuting the instructions in a system including the various vehiclehardware components in combination with the electronic controller. Oneor more of the method steps described herein may be omitted if desired.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific examples are notto be considered in a limiting sense, because numerous variations arepossible. For example, the above technology can be applied topowertrains that include different types of propulsion sources includingdifferent types of electric machines, engines, and/or drivetrains. Thesubject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

As used herein, the term “approximately” and “substantially” areconstrued to mean plus or minus five percent or less of the range orvalue unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A vehicle system, comprising: an electricmotor coupled to a locking mechanism of an inter-axle differential(IAD), wherein the inter-axle differential is configured to couple to afirst axle and a second axle and wherein the locking mechanism isconfigured to selectively disengage, and, in a disengaged configuration,the locking mechanism permits speed differentiation between the firstand second axles; and an electric motor brake coupled to the electricmotor and configured to selectively apply a brake torque to the electricmotor; wherein the locking mechanism is coaxial with an input interfaceof the IAD.
 2. The vehicle system of claim 1, wherein a central axis ofthe electric motor is parallel to a central axis of the lockingmechanism.
 3. The vehicle system of claim 1, wherein the lockingmechanism includes a ball ramp actuator that axially extends andretracts to engage and disengage the locking mechanism.
 4. The vehiclesystem of claim 1, wherein the first and second axles are included in atandem axle.
 5. The vehicle system of claim 1, wherein a first outputinterface coupled to the second axle is arranged coaxial to the inputinterface.
 6. The vehicle system of claim 5, wherein a second outputinterface that is coupled to the first axle is arranged perpendicular tothe input interface.
 7. The vehicle system of claim 1, wherein theelectric motor brake is a friction brake.
 8. The vehicle system of claim1, wherein the electric motor brake is an electromagnetic brake thatincludes coils and/or permanent magnets.
 9. The vehicle system of claim1, wherein the input interface is a yoke.
 10. A method for operation ofa vehicle system, comprising: energizing an electric motor to engage alocking mechanism in an inter-axle differential (IAD), wherein the IADis designed to couple to a first axle and a second axle and engagementof the locking mechanism prevents speed differentiation between thefirst axle and the second axle; activating an electric motor brakecoupled to the electric motor to apply a brake torque to the electricmotor and prevent back-driving of the electric motor; and de-energizingthe electric motor after the electric motor brake is activated.
 11. Themethod of claim 10, further comprising: deactivating the electric motorbrake to release the brake torque.
 12. The method of claim 10, whereinthe electric motor brake is a friction brake.
 13. The method of claim10, wherein the electric motor brake is an electromagnetic brake. 14.The method of claim 10, wherein the electric motor is energized inresponse to operator interaction with an input device.
 15. The method ofclaim 10, wherein the electric motor is automatically energized based onvehicle traction.
 16. A vehicle system, comprising: an electric motorcoupled to a locking mechanism of an inter-axle differential (IAD),wherein the IAD is configured to couple to a first axle and a secondaxle and the locking mechanism is configured to selectively disengage,and, in a disengaged configuration, the locking mechanism permits speeddifferentiation between the first and second axles; an electric motorbrake coupled to the electric motor; and a controller includingexecutable instructions that when executed cause the controller to:engage the locking mechanism to prevent speed differentiation betweenthe first axle and the second axle; and activate the electric motorbrake to apply a brake torque to the electric motor and preventback-driving of the electric motor; wherein the locking mechanism iscoaxial with an input interface of the IAD.
 17. The vehicle system ofclaim 16, wherein the electric motor brake is a friction brake or anelectromagnetic brake that includes coils and/or permanent magnets. 18.The vehicle system of claim 16, wherein the controller comprisesinstructions that when executed cause the controller to: de-energize theelectric motor after the electric motor brake is activated.
 19. Thevehicle system of claim 16, wherein the locking mechanism isautomatically engaged based on vehicle traction.
 20. The vehicle systemof claim 16, wherein the first and second axles are included in a tandemrear axle assembly.